Role of inspiratory capacity on dyspnea evaluation in COPD with or without emphysematous lesions: a pilot study

BACKGROUND: Since forced expiratory volume in 1 second (FEV(1)) shows a weak correlation with patients’ symptoms in COPD, some volume parameters may better reflect the change in dyspnea symptoms after treatment. In this article, we investigated the role of inspiratory capacity (IC) on dyspnea evaluation among COPD patients with or without emphysematous lesions. METHODS: In this prospective study, 124 patients with stable COPD were recruited. During the baseline visit, patients performed pulmonary function tests and dyspnea evaluation using the modified Medical Research Council (mMRC) scale. Partial patients underwent quantitative computerized tomography scans under physicians’ recommendations, and emphysematous changes were assessed using the emphysema index (EI; low attenuation area [LAA]% −950). These subjects were then divided into the emphysema-predominant group (LAA% −950≥9.9%) and the non-emphysema-predominant group (LAA% −950<9.9%). After treatment for ~1 month, subjects returned for reevaluation of both pulmonary function parameters and dyspnea severity. Correlation analysis between the change in IC (ΔIC) and dyspnea (ΔmMRC) was performed. RESULTS: Correlation analysis revealed that ΔIC was negatively correlated with ΔmMRC (correlation coefficient [cc], −0.490, P<0.001) in the total study population, which was stronger than that between ΔFEV(1) and ΔmMRC (cc, −0.305, P=0.001). Patients with absolute ΔmMRC >1 were more likely to exhibit a marked increase in IC (≥300 mL) than those with absolute ΔmMRC ≤1 (74.36% versus 35.29%; odds ratio [OR], 5.317; P<0.001). In the emphysema-predominant group, only ΔIC strongly correlated with ΔmMRC (cc, −0.459, P=0.005), while ΔFEV(1) did not (P>0.05). CONCLUSION: IC could serve as an effective complement to FEV(1) in COPD patients undergoing dyspnea evaluation after treatment. For COPD patients with predominant emphysematous lesions, an increase in IC is particularly more suitable for explaining dyspnea relief than FEV(1).